Localization of Disconnection Faults in PV Installations Using the Multiple Frequencies Injection Method

This paper proposes a method to detect disconnection faults and their exact location in PV systems. The proposed method injects multiple frequencies into a PV system with a transmitter and detects the injected signal using a receiver. The signal detected by the receiver exhibits different frequency characteristics on a disconnection failure. Based on this characteristic, a disconnection failure can be detected. In addition, by detecting the frequency radiated through the disconnection point, the exact disconnection point can be detected

Simulations to Eliminate Backflow Power in an Isolated Three-Port Bidirectional DC–DC Converter

The aim of this work was to eliminate the backflow power present in an isolated three-port DC–DC converter. Backflow power (which is an inherent property of phase-shifted DC–DC converters) is the major contributor of circulating current the converter, which in turn is known to be the leading cause of system loss. The dual phase shift (DPS) control scheme (which alters the transformer voltage waveform at the different winding terminals) was used to reduce the backflow power. Mathematical relations for the backflow power present in the three-port converter were derived. And from this equation, an operating point in which the backflow power is zero was also obtained. This condition for zero backflow power was confirmed by simulations on PSIM. Added to this were simulation results that show other operating conditions in which zero backflow power could be obtained in the converter. In addition, equations for the power processed at the different ports of the converter were also presented, and 3D plots were made to illustrate the variation of the power and backflow power with respect to the phase shift ratios of the DPS control scheme. It was observed that the backflow power can be totally removed from the three-port converter when using this control scheme

Simulations of the Comparative Study of the Single-Phase Shift and the Dual-Phase Shift-Controlled Triple Active Bridge Converter

This paper presents a comparative study between the traditional phase shift (also referred to as the Single-Phase Shift (SPS)) and the Dual-Phase Shift (DPS) controlled Triple Active Bridge (TAB) converter. Being a multi-port DC-DC converter with flexible power flow control and characterized by high power density, the TAB converter is applicable in almost any situation where a DC-DC converter is needed. With the availability of multiple control schemes, this work highlights the advantages and disadvantages of the most employed control scheme used on the TAB converter, in comparison with the DPS control scheme that has so far been applied only on Dual-Active Bridge (DAB) converters. As an example, for a TAB converter with a 14 kW maximum power capacity, the work sees the comparison of the backflow power, the maximum possible current, the processed power at the different ports of the converter, the transformer voltage and current waveforms, and the Total Harmonic Distortion (THD). Based on the results obtained, we found that the DPS-controlled TAB converter was more efficient when applied to the TAB converter compared to the traditional phase shift control algorithm

Novel Phase Shift Angle Compensation Method of DAB Converter Considering Parasitic Capacitance of SiC MOSFET

This study proposes a novel method to compensate phase shift angle of dual active bridge (DAB) converters by considering the parasitic capacitance of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). In general, the DAB converter bidirectionally transfers power between the primary and secondary sides using a phase shift angle. The conventional methods calculate the phase shift angle with an assumption of the instantaneous changes in the voltage and current. However, SiC MOSFETs used in a DAB converter have parasitic capacitances such as the input, output, and reverse transfer capacitance which affect the voltage and current leading to inaccurate phase shift angle calculation. For instance, the input parasitic capacitance delays the voltage slew rate between the drain and the source of the SiC MOSFET. Moreover, during the dead time, the output parasitic capacitance of the SiC MOSFET and leakage inductance in the DAB converter resonate, delaying the slew rates of both current and voltage. Therefore, this study analytically quantifies the effect of parasitic capacitances on the performance of the SiC DAB converter and proposes a novel phase shift angle compensation method. The proposed method was validated through simulations and experiments with a 4-kW SiC DAB converter prototype

Influence Analysis of SiC MOSFET’s Parasitic Capacitance on DAB Converter Output

This paper proposes the influence analysis of silicon carbide (SiC) MOSFET’s parasitic output capacitance on a dual active bridge (DAB) converter. Power converters are required for DC grids and energy storage. Because SiC metal-oxide-semiconductor FETs (MOSFETs) have lower on-state resistance and faster reverse recovery time than Si MOSFETs, they can be controlled with lower losses and higher frequencies. MOSFETs have a parasitic capacitance. Because of the output parasitic capacitance, the switch voltage does not rise instantaneously during switching but has a delay. The output parasitic capacitance of the switch depends on its drain-to-source voltage, and this parasitic capacitance affects the output of the DAB converter by delaying the switch voltage. In this paper, in order to analyze the effect of the parasitic capacitance on the DAB converter output, the delay time was calculated through a formula, and this value was compared with a simulated value. In addition, the effect of the parasitic capacitance of the SiC MOSFET on the output of the DAB converter was presented by comparing the actual output voltage with the ideal output voltage and analyzing the effect of the output voltage according to the delay

Effect of Chemical Agents on the Morphology and Chemical Structures of Microplastics

Increased demand for plastics leads to a large amount of plastic manufacturing, which is accompanied by inappropriate disposal of plastics. The by-products of these waste plastics are microplastics (MPs; less than 5 nm in size), which are produced because of various environmental and physicochemical factors, posing hazardous effects to the ecosystem, such as the death of marine organisms due to the swallowing of plastic specks of no nutritional value. Therefore, the collection, preparation, identification, and recycling of these microsized plastics have become imperative. The pretreatment of MPs requires numerous chemical agents comprising strong acids, bases, and oxidizing agents. However, there is limited research on the chemical resistance of various MPs to these substances to date. In this study, the chemical resistance of five species of MPs (high-density polyethylene, low-density polyethylene, polystyrene, polyethylene terephthalate, and polypropylene) to sulfuric acid, hydrochloric acid, hydrogen peroxide, potassium hydroxide, and sodium hydroxide was studied. The MPs were reacted with these chemical reagents at preset temperatures and durations, and variations in morphology and chemical structures were detected when the MPs were reacted with mineral acids, such as sulfuric acid. The data pertaining to these changes in MP properties could be a significant reference for future studies on MP pretreatment with strong acids, bases, and oxidizing agents

Adenoviral vector-mediated glucagon-like peptide 1 gene therapy improves glucose homeostasis in Zucker diabetic fatty rats

Background Glucagon-like peptide-1 (GLP-1) is a gut-derived incretin hormone that plays an important role in glucose homeostasis. Its functions include glucose-stimulated insulin secretion, suppression of glucagon secretion, deceleration of gastric emptying, and reduction in appetite and food intake. Despite the numerous antidiabetic properties of GLP-1, its therapeutic potential is limited by its short biological half-life due to rapid enzymatic degradation by dipeptidyl peptidase IV. The present study aimed to demonstrate the therapeutic effects of constitutively expressed GLP-1 in an overt type 2 diabetic animal model using an adenoviral vector system. Methods A novel plasmid (pAAV-ILGLP-1) and recombinant adenoviral vector (Ad-ILGLP-1) were constructed with the cytomegalovirus promoter and insulin leader sequence followed by GLP-1(7-37) cDNA. Results The results of an enzyme-linked immunosorbent assay showed significantly elevated levels of GLP-1(7-37) secreted by human embryonic kidney cells transfected with the construct containing the leader sequence. A single intravenous administration of Ad-ILGLP-1 into 12-week-old Zucker diabetic fatty (ZDF) rats, which have overt type 2 diabetes mellitus (T2DM), achieved near normoglycemia for 3 weeks and improved utilization of blood glucose in glucose tolerance tests. Circulating plasma levels of GLP-1 increased in GLP-1-treated ZDF rats, but diminished 21 days after treatment. When compared with controls, Ad-ILGLP-1-treated ZDF rats had a lower homeostasis model assessment for insulin resistance score indicating amelioration in insulin resistance. Immunohistochemical staining showed that cells expressing GLP-1 were found in the livers of GLP-1-treated ZDF rats. Conclusions These data suggest that GLP-1 gene therapy can improve glucose homeostasis in fully developed diabetic animal models and may be a promising treatment modality for T2DM in humans.This work was supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (KRF-2005-041-E00181)